In high pressure applications such as for fluid lines in an aircraft engine, fixed flange and swivel flange bolted face seal joints are commonly utilized to secure the fluid line. For example, in an aircraft engine, a fluid line typically extends to a port in the engine, and the line is secured to the engine at the location of the port so that fluid can flow through the line and into the engine. Providing a tight and secure fit between the fluid line and the engine clearly is important. Any leaks or other failures of the joint between the engine and the fluid line are highly undesirable.
In a known seal joint configuration, threaded fasteners (e.g., bolt plus a nut or an insert) around the periphery of the seal provide a distributed clamp force to resist fluid pressure that could separate the line from the engine and cause a leak. The number of fasteners and type of seal selected depend upon particular operating conditions.
With a fixed flange configuration, a flange is integral with the fluid line. Openings in the flange are aligned with openings in the engine outer surface, and bolts are inserted into respective aligned openings and tightened. A gasket typically is positioned between the flange and the engine so that a seal is formed between the flange and engine. If the fluid line cannot be easily twisted or bent, since the flange is fixed to the fluid line, it is necessary that the flange and flange openings be fabricated with very limited tolerances so that the proper alignment between the flange and the engine can be provided. Of course, manufacturing a flange and flange openings with very limited tolerances can be a cumbersome and time consuming process.
With a swivel flange configuration, a ferrule integral with the fluid line is provided, and the fluid line extends through a separate mating flange having openings to mate with openings in the engine. The mating flange is rotatable relative to the fluid line and is easily aligned with the bolt openings in the mating component, e.g., an aircraft engine.
Common applications for swivel flanges are high pressure hoses, which can fail if twisted to provide alignment, and rigid tubes, which commonly cannot be manufactured to the tolerance required for flange alignment. In both applications, the ferrule can mate with the seal surface in any circumferential orientation favorable to the fluid line and the swivel flange can then be rotated as required to align the bolt openings.
With a swivel flange, however, a gap at the fastener clamp load path is required to ensure that the clamping force is effective on the seal surface. Without a gap, none of the clamp force is transmitted to the seal and the ferrule can lift off under pressure. With a gap, all the clamp force is transmitted across the seal, but a bending load is placed on the fastener, e.g., bolt. Such a bending load is undesirable because such a load causes a concentrated stress much higher than the nominal clamp stress. Cyclic loading (pressure variations or external loads from the fluid line) has a significant effect on the fastener stress and could result in premature fatigue of the fasteners.
It would be desirable to provide a bolted seal joint assembly including a swivel flange which eliminates a need for fabricating tubes with fixed flanges having limited tolerances yet does not require a gap in the fastener load path to transmit all the clamp force across the seal. It also would be desirable to provide such a bolted seal joint assembly which does not have more components and is not significantly more expensive, in terms of both labor and material, than known swivel flange bolted seal joint assemblies.